Priority domains for protection switching processes

ABSTRACT

Embodiments of the invention describe apparatus, systems and methods for creating a protection switching domain having a control virtual local area network (vlan), a first set of high priority protected data vlans, and a second set of lower priority protected data vlans. When a fault is detected at a ring network, indicating a failed link between adjacent nodes, said fault is communicated to a master node of the ring network via the control vlan. 
     Embodiments of the invention allow a user to specify a priority for each of its domains on a given set of ring ports. The higher priority protected data domains are serviced to completion prior to servicing the lower priority protected data domains, ensuring that data traffic convergence time does not increase across these vlans.

FIELD

Embodiments of the invention relate to computer networking, and moreparticularly to establishing priority domains for protection switchingprocesses.

BACKGROUND

Bridged, layer-2 networks, such as Ethernet networks, provide servicesto areas where fiber optic lines do not extend and generally providehigh data capacity at a low cost. A problem with bus and ring networkslike the Ethernet is the possibility of a single point of failurecausing the system to breakdown. A common solution is to design thenetwork with redundant segments and loops so that there is more than oneroute to each node in a Synchronous Optical NETwork (SONET)-likeapproach (i.e., a layer-1 network). Redundancy and loops can, however,present another problem in which a broadcast packet or an unknownunicast packet results in a broadcast storm where each node receives andrebroadcasts the packet, causing potentially severe network congestion.

Current solutions for preventing single points of failures in ringnetworks, such as Ethernet Automatic Protection Switching (EAPS)systems, utilize an EAPS domain having a control virtual local areanetwork (vlan) and at least one protected data vlan. The EAPS domain isassociated with a master node linked to at least one transit node in aring network.

An EAPS system operates in conjunction with the master node to detect anetwork failure by means of control messages sent between the nodesusing the control vlan. During normal operation, the master node blocksthe protected data vlan traffic from traversing its secondary port.During a network failure, the master node reroutes the protected datavlan traffic through its secondary port. When the network is restored,the EAPS system operates in conjunction with the affected transit nodeto prevent looping by blocking the protected data vlan traffic fromtraversing its restored ring port until notified by the master node thatnormal operation has resumed.

Current solutions, however, encounter scaling issues with respect to thenumber of protected vlans. For EAPS solutions, as the number ofprotected vlans increase, data traffic convergence time also increasesacross all vlans. This is because EAPS processes the protected vlanssequentially. What is needed is an adaptable process for selecting whichvlans should be serviced first.

SUMMARY OF THE INVENTION

Embodiments of the invention describe apparatus, systems and methods forcreating a protection switching domain having a control virtual localarea network (vlan), a first set of high priority protected data vlans,and a second set of lower priority protected data vlans. Someembodiments of the invention may utilize more than two sets of protecteddata vlans. When a fault is detected at a ring network, indicating afailed link between adjacent nodes, said fault is communicated to amaster node of the ring network via the control vlan.

For the protected data vlans of the first set, the master node'ssecondary port is unblocked to traffic of at least one data vlan of thefirst set. A state of the ring network for the first set of data vlansis set to failed, and a forwarding database is flushed on the masternode and on the at least one transit node. The state of the ring networkfor the first set of data vlans is then set to complete when the ringnetwork is unbroken or the ring network has been restored and all nodesare communicating correctly.

For the protected data vlans of the second set, domain events of thedata vlans are queued until the state of the ring network for the firstset of data vlans is set to complete. Thus, embodiments of the inventionallow a user to specify a priority for each of its domains on a givenset of ring ports. The higher priority domains are serviced tocompletion prior to servicing the lower priority domains, ensuring thatdata traffic convergence time does not increase across these vlans.

BRIEF DESCRIPTION OF THE DRAWINGS

The following description includes discussion of figures havingillustrations given by way of example of implementations of embodimentsof the invention. The drawings should be understood by way of example,and not by way of limitation. As used herein, references to one or more“embodiments” are to be understood as describing a particular feature,structure, or characteristic included in at least one implementation ofthe invention. Thus, phrases such as “in one embodiment” or “in analternate embodiment” appearing herein describe various embodiments andimplementations of the invention, and do not necessarily all refer tothe same embodiment. However, they are also not necessarily mutuallyexclusive.

FIG. 1 is a block diagram illustrating an ethernet protection system forimplementing an embodiment of the invention.

FIG. 2 is a flow diagram of a process according to an embodiment of theinvention.

FIG. 3 is a block diagram of a network having a master node forexecuting a process according to an embodiment of the invention.

FIG. 4 illustrates a diagrammatic representation of a computer systemfor implementing an embodiment of the invention.

Descriptions of certain details and implementations follow, including adescription of the figures, which may depict some or all of theembodiments described below, as well as discussing other potentialembodiments or implementations of the inventive concepts presentedherein. An overview of embodiments of the invention is provided below,followed by a more detailed description with reference to the drawings

DETAILED DESCRIPTION

Embodiments of an apparatus, system and method for establishing prioritydomains for protection switching processes are described herein. In thefollowing description numerous specific details are set forth to providea thorough understanding of the embodiments. One skilled in the relevantart will recognize, however, that the techniques described herein can bepracticed without one or more of the specific details, or with othermethods, components, materials, etc. In other instances, well-knownstructures, materials, or operations are not shown or described indetail to avoid obscuring certain aspects.

Reference throughout this specification to “one embodiment” or “anembodiment” means that a particular feature, structure, orcharacteristic described in connection with the embodiment is includedin at least one embodiment of the present invention. Thus, theappearances of the phrases “in one embodiment” or “in an embodiment” invarious places throughout this specification are not necessarily allreferring to the same embodiment. Furthermore, the particular features,structures, or characteristics may be combined in any suitable manner inone or more embodiments.

FIG. 1 is a block diagram illustrating an ethernet protection system forimplementing an embodiment of the invention. System 100 includes of oneor more domains 101—e.g., an Ethernet Automatic Protection Switching(EAPS) domain or an Ethernet Ring Protection Switching (ERPS) domain. Inthis exemplary embodiment, domain 101 is shown as an EAPS domain.

Control VLAN 103 is created for each EAPS domain for the purpose ofsending and receiving EAPS system control messages 117. EAPS domain 101is created to protect a group of one or more data carrying VLANs 104.

EAPS system 100 operates on ring network 102. One node on ring network102 is designated as master node 105. The two ring ports on the masternode 105 are designated as primary port 106 and secondary port 107. Allother nodes on the ring network 102 are transit nodes 111 and each hasits respective ring ports 112. Each master node 105 and transit node 111has forwarding database (FDB), 108 and 113 respectively, in which theystore information about the network communication paths. The master node105 includes state register 109 for storing the state of ring network102. For the purpose of illustration, the states of the ring network 102are described as either as “failed,” meaning there is a fault or breakin the ring network 102, or as “complete,” meaning that the ring networkis unbroken or the ring network has been restored and all nodes arecommunicating correctly. Transit nodes 111 are shown to include stateregister 114, which stores the pre-forwarding state, and pre-forwardingtimer 115. The transit nodes 111 also have temporarily-blocked-portstorage area (TBP) 116 in which they store the identification of theport that is temporarily blocked.

Master node 105 and transit nodes 111 use control messages 117 tocommunicate via control VLAN 103. Some examples of control messages 117in embodiments include, for example, health-check messages, link-downmessages, and flush-FDB messages. In this embodiment, transit node 111recognizes a message sent on control VLAN 103 as control message 117because it has a special MAC (media access control) address thatcorresponds to an entry in forwarding database 113. The master node andthe transit nodes forward control message 117 prior to copying it to thecentral processing unit (CPU) of the node where, among other things, itmay be logged for use in troubleshooting.

In this embodiment, master node 105 includes hello-timer 118, which isthe clock for sending health-check control messages 117. Oncehello-timer 118 is started, it prompts master node 105 to sendhealth-check message 117 on control VLAN 103 at regular intervals—forexample every one second. Health-check message 117 is forwarded aroundring network 102 and returns to master node 105 nearly instantaneously.When master node 105 sends health-check message 117, it sets fail-timer110; should fail-timer 110 expire before the health-check message isreturned to master node 105, the master node determines that there is afault in ring network 102. Health-check messages 117 are sent evenduring a fault. When the fault is restored, master node 105 knowsimmediately because the return of the health-check message 117 isresumed.

In other embodiments of the invention, other methods for detecting afault in a ring network may be utilized. For example, if a node detectsa fault, it may send a link-down protocol data unit (PDU) on its otherring port; reception of a link-down PDU causes the master node to gointo a failed state, and open its secondary port. When the fault isrestored, nodes receive a health-check PDU to indicate that the ringnetwork is up. Other functionally equivalent processes for detecting afault may be used without deviating from the functionality ofembodiments described herein.

FIG. 2 is a flow diagram of a process according to an embodiment of theinvention. Flow diagrams as illustrated herein provide examples ofsequences of various process actions. Although shown in a particularsequence or order, unless otherwise specified, the order of the actionscan be modified. Thus, the illustrated implementations should beunderstood only as examples, and the illustrated processes can beperformed in a different order, and some actions may be performed inparallel. Additionally, one or more actions can be omitted in variousembodiments of the invention; thus, not all actions are required inevery implementation. Other process flows are possible.

In this embodiment, process 200 includes operations for establishing anautomatic protection switching domain for a ring network, 202. The ringnetwork includes a control vlan, and first set of protected data vlans(e.g., a high priority set of vlans) and a second set of protected datavlans (e.g., a lower priority set of vlans). Some embodiments of theinvention may utilize more than two sets of protected data vlans. Thering network is “complete” when all are communicating on the primaryport.

Said ring network includes a master node and a plurality of transitnodes. During normal operation, the master node blocks protected datavlan traffic from traversing the secondary port to prevent a loop. Inone embodiment, the control vlan is not blocked on the secondary port;only the protected data vlans are blocked. The ports may be blocked andunblocked using any means known in the art.

A fault is detected in the ring network, 204. When the master nodedetects a break in the ring, it unblocks the secondary port and allowsdata traffic to be transmitted and received through the secondary port.In one embodiment, the master node detects a fault in the ring networkusing polling or trapping via processes such EAPS. In other embodiments,the master node detects a fault in the ring network by verifying linkintegrity via processes, such as Connectivity Fault Management (CFM)protocols, for notifying fault handing processes such as EAPS orEthernet Ring Protection Switching ERPS. Other functionally equivalentprocesses for detecting a fault may be used without deviating from thefunctionality of embodiments described herein.

Said fault is communicated to the master node via the control vlan. Forexample, in polling processes, the master node periodically sends ahealth-check control message via the control vlan on the primary port.The health-check control message is one of the control messagesexchanged between the master node and the transit nodes. When the ringnetwork is complete, the health-check control message is returned to themaster node on its secondary port before a fail-timer expires, and themaster node determines that the ring network is complete. In oneembodiment, when there is a break in the ring network, the health-checkcontrol message is not returned to the master node before the fail-timerexpires.

For trapping processes, the master node may receive a link-down controlmessage from a transit node. The link-down control message is anotherone of the control messages exchanged between the master node and thetransit nodes. When a transit node detects a fault (i.e., a break in thering) on one of its ring ports, it may send a link-down control messageto the master node via the control vlan on its good port.

In this embodiment, the control vlan services the first set of protecteddata vlans before servicing the second set of protected vlans, 206.“Servicing” is shown to comprise operations including unblocking themaster node's secondary port to traffic of at least one data vlan of thefirst set, 212, when the state of the ring network for the first set ofdata vlans is set to “failed,” 210. A forwarding database is flushed onthe master node and on the at least one transit node, 214, which forcesall of the nodes to relearn the new path to the layer-2 end stations viathe reconfigured topology. The state of the ring network for the firstset of data vlans is set to complete, 216.

For the one or more protected data vlans of the second set, domainevents of the data vlans(s) of the second set are queued, 208, until thestate of the ring network for the first set of data vlans is set tocomplete. Then a similar “servicing” process is executed for the datavlans of the second set (e.g., the lower priority set).

Thus, processes according to embodiments of the invention, such as theexemplary process described above, allow a user to specify a priorityfor each of its domains on a given set of ring ports. The higherpriority domains are serviced to completion prior to servicing the lowerpriority domains, ensuring that data traffic convergence time does notincrease across these vlans.

FIG. 3 is a block diagram of a network having a master node forexecuting a process according to an embodiment of the invention. Network300 is shown to execute an EAPS protection process; however, asmentioned above, other embodiments may execute functionally equivalentprotection processes, such as an ERPS process.

Network 300 includes multiple EAPS domains on ring network 320 (shown toinclude nodes S1-S5) to improve efficiency by enabling spatial reuse ofthe ring network. EAPS domains 301 and 302 responsible for protectingits own group of data vlans. In this embodiment, EAPS domain 301includes high priority data vlans 304 and lower priority data vlans 305,while EAPS domain 302 includes high priority data vlans 306 and lowerpriority data vlans 307. Each EAPS domain includes a unique control vlan308/309 and master node 310/311. In other embodiments, EAPS domains 301and 302 can have the same master node.

Networks such as network 300 as shown may provide a user with fast L2redundancy for ring based topologies. On each switch a user creates anEAPS domain, which specifies 2 ring ports as well as a list of all vlansa particular EAPS domain will be protecting. When a failure occurs inring network 320, the EAPS domain spanning that ring take the necessaryaction to provide an alternative path for traffic to traverse. In doingthis, EAPS domains 301 and 302, on a per domain basis, take action onthe list of vlans protected by each EAPS domain affected by the failure.

In embodiments when data vlan sets 304/305 and 306/307 include largenumbers of vlans, there is a slight delay between the time the firstprotected vlan recovers and the last protected vlan recovers, sinceprocessing is handled sequentially. In this embodiment, users may dividetheir EAPS protected vlans into two or more domains, similar to how EAPSspatial reuse is configured on the same physical ring.

As described above, priorities may be assigned to each of these EAPSdomain groups. In some embodiments, high priority EAPS domains 304 and306 contain a small subset of protected vlans, while the lower prioritydomain 305 and 307 contain the bulk of protected vlans. This allows thesmall subset of protected vlans contained in the high priority domainsto get serviced first, resulting in faster, more predictable trafficconvergence times for this smaller set of vlans.

Thus, embodiments of the invention allow a user to specify a priorityfor each of its domains on a given set of ring ports. The higherpriority domains are serviced to completion prior to servicing the lowerpriority domains (as described, for example, by process 200 of FIG. 2).Internally within EAPS, an object called an EAPS domain group may becreated that identifies a physical ring to which all domains withmatching ring ports belong. The EAPS domain group is an abstraction thatmanages high and low priority domains for each physical ring. Alldomains, high and low, that have the same physical ring ports aremembers of the same domain group. When any of the EAPS domains of anEAPS domain group report a transition in their ring state, either “ringcomplete” or “ring failed,” the EAPS domain group transitions to thatparticular state. When the EAPS domain group detects a ring transition,EAPS may begin queuing lower priority domain events. These lowerpriority domain events remained queued until the higher priority domains(i.e., domains 304 and 306 in this example embodiment) have completedtransitioning to their new domain state. Once this occurs, lowerpriority events can now start processing events that cause lowerpriority domains (i.e., domains 305 and 307 in this example embodiment)to also transition their domain state.

Since asynchronous calls are made to hardware functions, anacknowledgement from hardware may be sent ensuring the hardwareoperation is completed. After the acknowledgement is received, an EAPSdomain may complete its state transition. Thus, as high priority domainsare in the process of transitioning due to a change in the ring state,the lower priority EAPS domains are queuing their events. As each highpriority domain finishes its transition to a steady state, a message issent to its EAPS domain group indicating that this particular domain isdone transitioning. When all high priority domains within an EAPS domaingroup have completed their transition, the EAPS domain group gives thesignal to begin processing lower priority EAPS domain events. Thisensures that all EAPS protected vlans that are part of high prioritydomains are serviced to completion first.

Before a high priority domain can complete its transition to a steadystate, it relies on messages from other nodes in the ring. This meansthat all nodes in a particular domain, high or low, enforce EAPS domainpriorities. Full data traffic convergence on a vlan is dependent on allnodes in the ring to have completed their necessary convergenceoperations in the correct priority order, be it blocking or unblocking aport, or flushing its FDB table.

FIG. 4 illustrates a diagrammatic representation of a machine in theexemplary form of computer system 400 within which a set ofinstructions, for causing the machine to perform any one or more of themethodologies discussed herein, may be executed. In alternativeembodiments, the machine may be connected (e.g., networked) to othermachines in a Local Area Network (LAN), an intranet, an extranet, or theInternet. The machine may operate in the capacity of a server or aclient machine in a client-server network environment, or as a peermachine in a peer-to-peer (or distributed) network environment. Themachine may be a personal computer (PC), a tablet PC, a set-top box(STB), a Personal Digital Assistant (PDA), a cellular telephone, or anymachine capable of executing a set of instructions (sequential orotherwise) that specify actions to be taken by that machine. Further,while only a single machine is illustrated, the term “machine” shallalso be taken to include any collection of machines (e.g., computers)that individually or jointly execute a set (or multiple sets) ofinstructions to perform any one or more of the methodologies discussedherein.

Exemplary computer system 400 includes processor 402, main memory 404(e.g., read-only memory (ROM), flash memory, dynamic random accessmemory (DRAM) such as synchronous DRAM (SDRAM) or Rambus DRAM (RDRAM),etc.), static memory 406 (e.g., flash memory, static random accessmemory (SRAM), etc.), and secondary memory 418 (e.g., a data storagedevice), which communicate with each other via bus 408.

Processor 402 represents one or more general-purpose processing devicessuch as a microprocessor, central processing unit, or the like. Moreparticularly, processor 402 may be a complex instruction set computing(CISC) microprocessor, reduced instruction set computing (RISC)microprocessor, very long instruction word (VLIW) microprocessor, aprocessor implementing other instruction sets, or processorsimplementing a combination of instruction sets. Processor 402 may alsobe one or more special-purpose processing devices such as an applicationspecific integrated circuit (ASIC), a field programmable gate array(FPGA), a digital signal processor (DSP), network processor, or thelike. Processor 402 is configured to execute processing logic/modules426 for performing the operations such as those described by process 200of FIG. 2.

Computer system 400 may further include network interface device 416.The computer system also may include video display unit 410 (e.g., aliquid crystal display (LCD) or a cathode ray tube (CRT)), alphanumericinput device 412 (e.g., a keyboard), and cursor control device 414(e.g., a mouse).

Secondary memory 418 may include machine-readable storage medium (ormore specifically a computer-readable storage medium) 424 on which isstored one or more sets of instructions (e.g., software 422) embodyingany one or more of the methodologies or functions described herein.Software 422 may also reside, completely or at least partially, withinmain memory 404 and/or within processing device 402 during executionthereof by computer system 400, main memory 404 and processing device402 also constituting machine-readable storage media. The software mayfurther be transmitted or received over network 420 via networkinterface device 416.

Various components referred to above as processes, servers, or toolsdescribed herein may be a means for performing the functions described.Each component described herein includes software or hardware, or acombination of these. Each and all components may be implemented assoftware modules, hardware modules, special-purpose hardware (e.g.,application specific hardware, ASICs, DSPs, etc.), embedded controllers,hardwired circuitry, hardware logic, etc. Software content (e.g., data,instructions, configuration) may be provided via an article ofmanufacture including a non-transitory, tangible computer or machinereadable storage medium, which provides content that representsinstructions that can be executed. The content may result in a computerperforming various functions/operations described herein.

A computer readable non-transitory storage medium includes any mechanismthat provides (i.e., stores and/or transmits) information in a formaccessible by a computer (e.g., computing device, electronic system,etc.), such as recordable/non-recordable media (e.g., read only memory(ROM), random access memory (RAM), magnetic disk storage media, opticalstorage media, flash memory devices, etc.). The content may be directlyexecutable (“object” or “executable” form), source code, or differencecode (“delta” or “patch” code). A computer readable non-transitorystorage medium may also include a storage or database from which contentcan be downloaded. Said computer readable medium may also include adevice or product having content stored thereon at a time of sale ordelivery. Thus, delivering a device with stored content, or offeringcontent for download over a communication medium may be understood asproviding an article of manufacture with such content described herein.

The above description of illustrated embodiments of the invention,including what is described in the Abstract, is not intended to beexhaustive or to limit the invention to the precise forms disclosed.While specific embodiments of, and examples for, the invention aredescribed herein for illustrative purposes, various modifications arepossible within the scope of the invention, as those skilled in therelevant art will recognize.

These modifications can be made to the invention in light of the abovedetailed description. The terms used in the following claims should notbe construed to limit the invention to the specific embodimentsdisclosed in the specification. Rather, the scope of the invention is tobe determined entirely by the following claims, which are to beconstrued in accordance with established doctrines of claiminterpretation.

1. A method comprising: creating a protection switching domain having acontrol virtual local area network (vlan), a first set of one or moreprotected data vlans, and a second set of one or more protected datavlans; detecting a fault in a ring network, the ring network having amaster node connected to at least one transit node, each node linked toan adjacent node by at least one of a primary port or a secondary port,the fault indicating a failed link between adjacent nodes; communicatingthe fault to the master node via the control vlan; for the one or moreprotected data vlans of the first set: unblocking the master node'ssecondary port to traffic of at least one data vlan of the first set;setting a state of the ring network for the first set of data vlans tofailed; flushing a forwarding database on the master node and on the atleast one transit node; and setting the state of the ring network forthe first set of data vlans to complete; and for the one or moreprotected data vlans of the second set, queuing domain events of thedata vlans(s) of the second set until the state of the ring network forthe first set of data vlans is set to complete.
 2. The method of claim1, wherein the first set of protected data vlan(s) includes prioritydata indicating a higher priority that the second set of protected datavlan(s).
 3. The method of claim 1, wherein the first set of protecteddata vlan(s) comprises less data vlans than the second set of protecteddata vlan(s).
 4. The method of claim 1, wherein the protection switchingdomain comprises an Ethernet Automatic Protection Switching (EAPS)domain.
 5. The method of claim 4, wherein detecting the fault comprisesthe master node polling the ring network to determine whether the ringnetwork is complete.
 6. The method of claim 1, wherein the protectionswitching domain comprises an Ethernet Ring Protection Switching (ERPS)domain.
 7. A system comprising: a memory to store a forwarding database;and a network controller to: create a protection switching domain havinga control virtual local area network (vlan), a first set of one or moreprotected data vlans, and a second set of one or more protected datavlans; detect a fault in a ring network, the ring network having amaster node connected to at least one transit node, each node linked toan adjacent node by at least one of a primary port or a secondary port,the fault indicating a failed link between adjacent nodes; communicatethe fault to the master node via the control vlan; for the one or moreprotected data vlans of the first set: unblock the master node'ssecondary port to traffic of at least one data vlan of the first set;set a state of the ring network for the first set of data vlans tofailed; flush the forwarding database on the master node and on the atleast one transit node; and set the state of the ring network for thefirst set of data vlans to complete; and for the one or more protecteddata vlans of the second set, queue domain events of the data vlans(s)of the second set until the state of the ring network for the first setof data vlans is set to complete.
 8. The system of claim 7, wherein thefirst set of protected data vlan(s) includes priority data indicating ahigher priority that the second set of protected data vlan(s).
 9. Thesystem of claim 7, wherein the first set of protected data vlan(s)comprises less data vlans than the second set of protected data vlan(s).10. The system of claim 7, wherein the protection switching domaincomprises an Ethernet Automatic Protection Switching (EAPS) domain. 11.The system of claim 10, wherein detecting the fault comprises the masternode polling the ring network to determine whether the ring network iscomplete.
 12. The system of claim 7, wherein the protection switchingdomain comprises an Ethernet Ring Protection Switching (ERPS) domain.13. A machine-readable storage medium having computer executableinstructions stored thereon that, when executed, cause a processor toperform a method comprising: creating a protection switching domainhaving a control virtual local area network (vlan), a first set of oneor more protected data vlans, and a second set of one or more protecteddata vlans; detecting a fault in a ring network, the ring network havinga master node connected to at least one transit node, each node linkedto an adjacent node by at least one of a primary port or a secondaryport, the fault indicating a failed link between adjacent nodes;communicating the fault to the master node via the control vlan; for theone or more protected data vlans of the first set: unblocking the masternode's secondary port to traffic of at least one data vlan of the firstset; setting a state of the ring network for the first set of data vlansto failed; flushing a forwarding database on the master node and on theat least one transit node; and setting the state of the ring network forthe first set of data vlans to complete; and for the one or moreprotected data vlans of the second set, queuing domain events of thedata vlans(s) of the second set until the state of the ring network forthe first set of data vlans is set to complete.
 14. The machine-readablestorage medium of claim 13, wherein the first set of protected datavlan(s) includes priority data indicating a higher priority that thesecond set of protected data vlan(s).
 15. The machine-readable storagemedium of claim 13, wherein the first set of protected data vlan(s)comprises less data vlans than the second set of protected data vlan(s).16. The machine-readable storage medium of claim 13, wherein theprotection switching domain comprises an Ethernet Automatic ProtectionSwitching (EAPS) domain.
 17. The machine-readable storage medium ofclaim 16, wherein detecting the fault comprises the master node pollingthe ring network to determine whether the ring network is complete. 18.The machine-readable storage medium of claim 13, wherein the protectionswitching domain comprises an Ethernet Ring Protection Switching (ERPS)domain.